Structure of the beta-1,3-1,4-glucanase gene of Bacillus macerans: homologies to other beta-glucanases

Abstract

The nucleotide sequence of an 852 base pair (bp) DNA fragment containing the entire gene coding for thermostable beta-1,3-1,4-glucanase of Bacillus macerans has been determined. The bglM gene comprises an open reading frame (ORF) of 711 bp (237 codons) starting with ATG at position 93 and extending to the translational stop codon TAA at position 804. The deduced amino acid sequence of the mature protein shows 70% homology to published sequences of mesophilic beta-1,3-1,4-glucanases from B. subtilis and B. amyloliquefaciens. The sequence coding for mature beta-glucanase is preceded by a putative signal peptide of 25 amino acid residues, and a sequence resembling a ribosome-binding site (GGAGG) before the initiation codon. By contrast with the processed protein, the N-terminal amino acid sequence constituting the putative leader peptide bears no or only weak homology to signal peptides of mesophilic Bacillus endo-beta-glucanases. The B. macerans signal peptide appears to be functional in exporting the enzyme to the periplasm in E. coli. More than 50% of the whole glucanase activity was localized in the periplasmic space and in the supernatant. Whereas homology to endo-1,4-beta-glucanases is completely lacking, a weak amino acid homology between the sequence surrounding the active site of phage T4 lysozyme and a sequence spanning residues 126 through 161 of B. macerans endo-beta-glucanase could be identified.